Method and apparatus for offset xerographic reproduction

ABSTRACT

A method and apparatus for transferring a developed xerographic powder image from a photoconductive surface to a final support material such as paper by contacting the powder image with elastomeric material under pressure to encapture the developed powder image due to the deformation of the elastomeric member and then transferring the powder image from the elastomeric member onto a paper support material by heat and pressure. In one example of the invention the elastomeric member is in the form of a belt while in another example of the invention the elastomeric member is formed on a drum surface. The paper support material may be preheated in one case prior to the pressure transfer of the powder image or alternatively heat may be applied simultaneously at the contacting surfaces transferring the powder image from the elastomeric member onto the paper support material.

D United States Patent w13,s91,276

[72] Inventor J hn F. Byrne 3,094,909 6/1963 Szekeres v. 355/3 Worthington, Ohio 3,267,840 8/1966 Tsutoma Honma et al. 355/3 (X) [2]] Appl. No. 686.930 3.320.061 5/1967 Gundlach 355/17 (X) {22] Filed Nov. 30,1967 3,399,611 9/1968 Lusher r. 355/4 lily Primary Examiner$amuel S. Matthews [73] Asstgnee Xerox Corporation Rocha" Assistant Exammer-Robert P1Gremer Anorneys- Norman E. Schrader, James J Ralabate and Ronald Zibelli [54] METHOD AND APPARATUS FOR OFFSET XEROGRAPIIIC REPRODUCTION C 3 mm m ABSTRACT: A method and apparatus for transferring a U.S. developed xe ographic powdgr image from a photoconducflye 1 17/21, 355/17 surface to a final support material such as paper by contacting [51] Int. Cl 0033 15/00, the powder image with elastomeric material under pressure to 8 l3/l4 encapture the developed powder image due to the deforma 0' r. 6, ion of the clastomeric member and then ransfen-ing he 17, 117/175. 2| 1 96/14 powder image from the elastomeric member onto a paper suprt material by heat and pressure. In one example of the in- [56] R'knm cued 5:11am the elastomeric member is in the form of a belt while UNITED STATES PATENTS in another example of the invention the elastomeric member is 2,990,278 6/1961 Carlson .r 1 I 7/ l 7.5 (X) formed on a drum surface. The paper support material may be 3,019,126 [/1962 Bartholomew... 117/17 preheated in one case prior to the pressure transfer of the 3,l97,324 7/ I965 Brooks l l 1 17/21 powder image or alternatively heat may be applied simultane- 3,374,769 3/1968 Carlson 1. 1 18/641 ously at the contacting surfaces transferring the powder image 3,506,347 4/1970 Carlson 355/3 from the elastomeric member onto the paper support materi- 3,051,568 8/1962 Kaprelian 355/17 (X) a].

PATENTEU JUL 6 an INVENTOR.

F. EYRNE UOHN 1; :af %w/ METBOD AND APPARATUS FOR OFFSET XEROGRAPHIC REPRODUCTION This invention relates to method and apparatus for transferring a xerographic powder image from a rerogrsphic plate to a support material and, in particular, to method and apparatus for transferring a high percentage of the xerographic powder.

More specifically, this invention relates to an improved method for transferring an extremely high percentage of a itcrographic powder image from a photoconductive surface to a support material to produce what is herein referred to as a quality image transfer. In the process of tterography, a plate, comprising a conductive baclting upon which is placed a photoconductive insulating material, is charged uniformly and the photoconductive surface then exposed to a light image. The photoconductive coating becomes conductive under the influence of the light image so as to selectively dissipate the electrostatic charge found thereon to produce what is known as a latent image. The latent image is developed by means of a variety of pigmented resins which have been specifically de eloped for this purpose. The pigmented resins, or, as herein referred to, "toners," are electrostatically attracted to the latent image on the photoconductive surface in proportion to the amount of charge found thereon. Areas of small charge concentration become areas of low toner density while areas of greater charge concentration become proportionally more dense.

The conventional method of transferring a developed xerographic image from a photoconductive surface to a support material is by electrostatic attraction. That is, a high electrostatic force field is created at the scrographic transfer station having a magnitude capable of overcoming the forces holding the serographic powder image to the photoconductive surface. Electrostatic transfer is, as attested to by its commercial acceptance, a highly satisfactory means of transferring a developed xerographic image. to a paper support material. A corona generating device is positioned at the transfer station to impart an electrical charge to the paper support material of sufficient strength to attract toner particles from the photoconductor. The magnitude of the charge required to ef fect image transfer is dependent upon many variables. it has been found, however, that because of the nature of the elcc trostatic transfer operation some residual developing material re mains behind on the photoconductivc surface after transfer. That is, the electrostatic transfer force applied to the support material effects transfer of a preponderance of the developed powder image but some toner particles, possessing a higher magnitude of force than the electrostatic transfer force, remain behind on the photoconductive surface.

As can be sten, high quality image transfer in which fine details and halftones are discemable cannot be efficiently roduced by conventional electrostatic transfer means because some of the image is left behind during the transfer operation. Furthermore. the removal and handling of residual toner left on the plate surface creates another unwanted problem in xerography.

With the advent of new serographic techniques and materials. it is now possible to serographically expose and develop images of finer detail than had heretofore been possible. However, these high quality images are of little value unless they can be efficiently transferred to a support material. That is, if art of the image is left behind during the transfer operation, the quality of the copy produced will be reduced by the amount of the residuum found on the plate surface.

It is therefore an object of this invention to improve method and apparatus for transferring a developed xerographic powder image from a photoconductive surface to a support material.

it is another object of this invention to transfer a xerographic powder image from a photoreceptor surface to a suport material with a minimum ofimage degradation.

Another object of this invention is to im rove fiitl:""'l an apparatus for effecting high-quality image transfer of a developed lerographic image.

A still further object of this invention is to transfer substantially all of: developed powder image from a photoconductivc surface to a final support material.

Yet another object of this invention is to reduce the amount of residual toner on a serographic plate after transfer.

These and other objects of this invention are attained by method and apparatus capable of initially removing an extremely high percentage of a developed xerographit; image from a photoreccptive surface by encapturing the image in a resilient, heat-resistant, intermediate blanket and transporting said image to a remote final transfer station. At the second or final transfer station, the image is transferred from the intermediate blanket to a support material by means of a heat transfer operation.

For a better understanding of the invention as well at other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein;

FIG. I is a schematic sectional view ofa conventional type of iterographic processing machine adapted to perform the two-step transfer method ofthe present invention;

Fl(]. 2 is a schematic embodiment of the present invention in which a transfer blanket is shown in drum configuration; and

HO. 3 is another partial embodiment showing a conductive heating means at the final transfer station.

HO. 1 shows an automatic iterographic apparatus employ ing a photoconductive surface which is formed in drum configuration. The drum to comprises a pholoconductive lightsensitive receiving surface H which is placed on a conductive backing ii. The drum is mounted on shaft I3 journaled in a machine frame (not shown) so as to rotate in a clockwise direction as indicated by the arrow. Rotation of the drum causes the drum surface to sequentially pass a plurality of xerographic processing stations. The drum is rotated at a constant rate through the action of synchronous drive motor H.

For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the drum surface may be described functionally as follows:

A charging station [5 at which a uniform electrostatic charge is deposited on the photoconductive layer of the xerographic drum;

An exposure station 26 at which alight image or radiation pattern of copy to be reproduced is projected onto the drum surface to dissipate the drum charge in the exposed areas thereon so as to form a latent electrostatic image of the copy to be reproduced;

A developing station 17, at which point, triboelectrically charged toner particles are brought into close proximity to the oppositely charged latent image found on the photoconduetive surface. The oppositely charged toner particles are attracted to the charged areas on the drum surface thereby developing the latent image;

A transfer station 18 where the xerographic powder image is electrostatically transferred from the drum surface to an intermediate support material; and,

A drum-cleaning and discharge station 19 capable of removing residual toner particles found on the drum surface after transfer.

in general, the charging apparatus located at station 15 may be of the type disclosed in Walltup US. Pat. No. 2,777,957, and includes a corona discharge array 20 of one or more corona discharge electrodes that extend transversely across the drum surface and are energized from a high-potential source (not shown) and are substantially enclosed in a shielding member IL The drum, which is being rotated past the charging station, is sprayed with sufficient charged ions to uniformly charge the drum surface at a relatively high poten tia .subscquent thereto in the path of motion of the zero drum. is exposure station 16. This exposure station one of a number of types of mechanisms or the like :d to pltljCCl a light image of the copy onto the onductive surface. An original document is placed on )f'. 22 and the transport is driven at synchronous speed re iterographic drum surface by means of motor 23. A iurce 24 illuminates the original document and the light is transported through optical system 25 and placed on im system at scanning slit 26. A pn'sm 9 reverses the and reflects it through the slit l6 onto drum If). mom to the exposure station is developing station 17 ipcr housing 27 contains a lower sump portion 28 in an accumulation of developing material is housed. A .-type conveyor 29, having a suitable driving means motor 30, is used to transport the developing material upper part of the developer housing where it is cascaded over a hopper chute onto the xerographic drum. As the ping material is cascaded over the drum, toner particles :ctrostatically attracted from the carrier component of 'velopcr material to the drum surface to develop tht: image found thereon. Dcnudcd carrier particles flow the drum surface and are once again returned to the iper housing sump. As toner images are formed, addi toncr particles may be supplied to the developer matcri roportion to the amount oftoncr deposited on the drum iis purpose there is provided a container Si by which 32. can be added to the developing material as needed, ner being added at a rate determined by control gate 33. er development, the image thus formed is transferred at n III, the operation of which will be explained in further below. final station in the present device is a drum-cleaning lischarge station where residual powder, if any, which ns on the itcrographicdrum after transfer is removed by ng brushes 35 driven by motor 37. A conditioning run is positioned adjacent to the cleaning brushes which s the residual toner remaining on the drum with ions havcharge opposite to that of the residual toner. This op :chargc tends to neutralize the residuum thereby making blc highly efficient drum cleaning. It should be noted that leaning station, as shown in this preferred embodiment, e eliminated in the present invention because ofthe elTr y ofthe transfer operation. sically, the transfer operation of the present invention is :d out in two distinct steps. Initially, the itcrographic ler image is pressure transferred from a photoreceptor to nterrnediate blanket, the blanket being adapted to tanically remove a powder image from a xerographic The transfer blanket is described in further detail below. intermediate blanket is then transported to a final transfer )n located at any suitable distance from the plate surface. use the toner powder is mechanically affixed to the blanthe distance in time and transit to the final support station no way restrictive. A wide flexibility in machine configun is thereby afforded by use of this intermediate transfer ket. The final transfer step to a final support material is mplished by a heat transfer operation in which the xerohie powder is melted sufficiently to bond to the support :rial. ie transfer blanket is constructed of a heat-resistive :rial having a resiliency such that the blanket is able to rm around iterographic powder particles making up a graphic image. The blanket is biased into contact with an ;e-bcaring plate with sufficient force to cause defamation c blanket material. The biasing force is then released and deformed blanket begins recovery. However, complete vcry is prevented by the particulate material enfoldcd or :pped therein. Sufficient holding force is exerted by the tent blanket material upon the powder particles to overe the heretofore mentioned mechanical and electrostatic :s holding them to the plate. The powder image cnfoldcd ie blanket material is remo ed from the plate with the kct.

Blankets, similar to the one herein described, have been made by casting a silicon: gum rubber on a soft metal substrate such as aluminum or brass to form an endless belt Developed images having resolutions in the nature of 40 line pairs pcr millimeter have been transferred to the silicone blankets using a pressure of between S nd I0 lbs, per linear inch. It was found that about 95 percent image transfer was effected at transfer speed in excess of inches per second. lllankets having a hardness of between 15 and duromcters were tested under the above mentioned conditions with little noticeable effect on the quality of the transfer or the efl'icicm cy of the operation. A gum rubber suitable for use as a transfer blanket material is manufactured by the General [ilectric Company under the trade name RTV-6l 5A Referring once again to FIG. I, a pickof'f blanket 40 is shown positioned in the transfer station 18. Blanket 40 acls as an intermediate support material to which a developed xerographic image is transferred from drum to during the first step of the two-step transfer operation. A drive motor 43, acting through drive roller 44, moves the blanket at synchronous speeds with thc peripheral drum surface so that no relative motion exists between the two which could cause offsetting of the image during the initial transfer slcp. Although not shown any convenient belt-tensioning device can be employed to prevent belt slippage during the transfer operation. A pair of rollers 4i and 42, respectively, fold the blanket in contact with the drum surface over a portion of the drum arc. The rollers are biased into contact with the drum by means of a pressure exerting element 45. The pressurecxcrting element is housed within a casting 46 permanently affixed to the machine frame The pressure-exerting clement comprises in regulating screw 47 positioned on shaft 48. lly turning control knob 49, located at the end of shaft 48, the position of bifurcated member 50 can be adjusted to control the amount of force exerted upon the blanket. Part of shaft 48 is surrounded by a compression spring 5| which acts upon the rollers to supply the necessary biasing force.

The final support material employed in the preferred embodiment is paper web 55. Roll 56 supplies a continuous web of support material to a series of feed rollers 57 and 58, respectively. The feed rollers guide the paper support mate rial into contact with the intermediate image bearing transfer blanket. A pressure roller 59 which is also being driven at the same peripheral speed of the blanket, is mounted in close proximity to the blanket and is adapted to urge the paper sup port material into pressure contact therewith The movement of the web material is synchronized with the movement of the blanket by means of drive motor 60 acting through pickup roll (it. Positioned adjacent to the point of contact between the support material and the transfer blanket is a heating unit ()1. The heating unit is positioned so that the web of support material is placed in thermal contact therewith prior to its contacting the imagobearing support blanket. Sufficient heat energy is transferred to the support material to cause the xerographic powder to melt or partially melt when brought into contact therewith. Although heating unit 6! is of the o en type. it should be clear that any heating de ice capable of raising the temperature of the suppo t material to a level sufficicnt to effect transfer of a xerographic powder image can he so utilized.

It should be noted that the silicone rubber blanket is adhe sive by nature. On the other hand, a paper support material it made of fibrous material to which heated toner particles wil readily bond. A relatively small force normal to the blanke surface is all that is required to separate the heated scro graphic powder image from the adhesive blanket. Although i' is contemplated that sufficient heat energy will be transferrcc during the final transfer operation to produce fusing of tht image to the final support material, it is, however, quite feasi ble to obtain transfer to thc final support material at tempera tures below the fusing temperature of the toner.

FIG. 2 is a modified embodiment of the present invention ir which the transfer blanket 40 is mounted in drum configura tion. Drum is rotatably mounted in the machine frame no shown) and driven at the same peripheral speed as the xerographic drum ill. The intermediate transfer drum is biased into contact with the xerographic drum thereby effecting a ressure transfer as previously described. The image is next transported to a final transfer station '71. The paper support is shown being guided through the final transfer station by means of guide rolls 57 and 58. A roller 7l capable of being heated internally is positioned at the final transfer station and is mounted in close proximity to drum 70 so that a paper suport 55 passing thcrebetween is pressed into contact with the transfer blanket 40. it has been found that a combination of heat and pressure, as herein described, produces a rapid and efficient transfer of the powder image to the final support t material. A lOO percent image transfer to a paper support material has been produced at transfer speeds in excess of inches per second by contacting the nonimage side of the paper support material with a roll being maintained at a tempcraturc of 450 F. while applying a pressure of I00 lbs. per linear inch.

Oftcntimcs these relatively high-transfer temperatures can not be utilized because of the nature of the support material being processed. lt is therefore desirous to utilize lower tem pcratures during the final heat transfer stepv Referring now to H6. 3, a partial schematic of a modified embodiment of the final transfer operation is shown therein. A heater 80 comprising a heat-insulated enclosure 81 and a cuwcd heat transfer station 81, is shown positioned imrnediately below transfer blanket in the final transfer station. The heat transfer surface 82 is made of a relatively smooth material having high thermal conductivity over which sup ort material can be readily advanced. The heat transfer surface is converted upwardly with an appropriate curvature so that the advancing support material is forced into close sliding contact therewith thereby producing good conductivc heat flow between thetwo contacting surfaces. A heat source 83 is positioned internal the heater enclosure and is opcratively connected to control means (not shown) to maintain the heat transfer surface at a predetermined temperature levcl.

Blanket 40 is brought into close proximity with the heat transfer surface by means of rollers 84 and 85. The web of support material 55 which is being guided over the heated platen surface by rollers 57 and 58, respectively, is force into close sliding contact with the curved platen surface by the transfer blanket. Heat is conducted through the support material to the exposed portion of the xerographic powder image and trapped within the blanket material. Sufficient heat is transferred to the powder image to cause it to coalesce or adhere to the paper support material with sufficient strength so that image separation is effected when the paper is removed from contact with the blanket.

It should be noted that the two-step transfer operation of the present invention is extremely well suited to effect image transfer anywhere around the drum periphery. Although the initial transfer step is shown taking place at the 6 o'clock posiion, it should be clear that the present apparatus is in no way so restricted. initial transfer at any drum position is quite feasible. A further advantage of this transfer method is its capability of transporting a powder image to a remote final transfer station thereby enabling the paper handling equipment. fusing e uipment and the like to be conveniently located at some distance from the photoreceptlve surface. in other words, the present invention enables quality transfer to be performed at stations remote from a xerographlc drum or the like thereby giving a wide freedom of machine design heretofore unknown in the art.

While this Invention has been described with reference to the structure disclosed herein. it is not confined to the details as set forth, and this application is intended to cover such modificalitmtt or changes as may come within the purposes of the improvements or the scope ofthe following claims.

I claim I. The method of transferring a heat-fusible powder image of toner particles from a xcrographic plate to a paper support material including pressing a resilient merrxber into contact with the image- 5 bearing xerographic ft ate with sufficient force to cause the member to deform about the powder image,

releasing the deforming pressure exerted on said member whereby the powder particles forming the image are enfolded within the resilient member applying aufTtcicnt heat energy to a paper sup ort material such that upon contact with the powder image cnfolded in said member the toner particles melt,

immediately contacting the toner particles with the paper support material causing the toner particles to melt and coalesce and transfer from the member to the support material. 2. The method of claim I wherein said support material is maintained at a temperature sufficient to cause the owder image to fuse to the su ort material when contacted 0 therewith.

3. The method of claim I wherein said resilient member is comprised of a silicone gum rubber having a hardness rangin from about l5 to about 35 duromctcrs east on a flexible suh strate.

4. The method of claim 3 wherein the heat-fusible powder image is heated to a temperature below its fusing temperature 5. The method of claim 4 having the further step of pressing the support material into contact with said member with sulficient force to fix the powder image to the support material.

6. in the process of xcrography wherein an electrostatically charged aerographic plate is exposed to a projected light image to form an electrostatic latent image on the plate corresponding to the projcctcd image and the plate is developed with heat-fusible toner particles attracted to the latent image to form a rterographic powder image corresponding to the projectcd image, the method of transferring and fixing the powder image to a paper support material comprising pressing a silicone rubber member into intimate contact with the powder bearing xerographic plate with sufficient force to cause the member to deform around said image,

releasing the deforming force exerted on said member whereby the recovering resilient member enfolds the powder image therein,

removing the image-bearing resilient member from the xerographie plate,

heating a paper support material to a temperature sufficient to melt said xerographic powder when brought into contact therewith; and

immediately pressing the heated paper support material into intimate contact with the image bearing resilient member with lufficient force to cause the powder image to adhere to the support material and become fixed thereto.

7. Apparatus for transferring a xerographic powder image 55 of toner particles from a'photoconductive plate to a a er support material and fixing the image thereon including a resilient member arranged to be placed in contact with the photoconduetive plate,

means to exert a bias pressure on the resilient member into pressure contact with e photocontluctivc plate with suf' l'tclent force to cause the member to deform about the powder image for a predetermined time and then to release the deforming pressure exerted on said member whereby the member recovers sufficiently to entrap powder particles therein,

means for transporting a paper support material into contact with the member carrying powder particles, and means to raise the temperature of the paper support material sufficiently immediately before contact of the support material with the powder particles such that upon contact said powder particles are transferred from the resilient member to the support material and fitted thereon.

5. The apparatus ofclaim 7 wherein said member comprises silicone gum rubber having a hardness ranging from about l5 to about 35 durometent.

9. A paratus for transferring xerographic powder image om a rotating photoconduetive drum to a final support militia] and fixing said powder image to the final support iatcrial including a resilient member being arranged to contact the photoconductive drum.

drive means [or moving said member at the name peripheral speed as the drum,

means to place the resilient member into pressure contact with the drum with aufl'ieient force to cause the member to deform about the powder image for a predetermined time and then, in release the deforming pressure exerted on said member whereby the member recovers [tim ciently to entrap powder particle: therein,

means to move I final lupport material into contact with the owder image enfolded in said member. and means to heat the xerogrnphlc powder image while in euntact with the final support material whereby the powder image coalesce: to the final support material.

10. The apparatus of claim 9 wherein said member com prises silicone gum rubber.

1!. The apparatus olclaim [0 wherein said member is sup ported on a cylindrical drum.

1!. The apparatus of claim [0 including meant to raise the temperature of the final aupport material to a level whereby the powder image being transferred is fused to said support material.

13 The apparatus of claim I] having further means to force the final support material into contact with the silicone gum rubber member with suflieient pressure to cause the heated toner to bond to the final support material.

I. The apparatus of claim 10 wherein the final support material ll held in contact with the lilicone rubber member by l heated platen arranged to lupport the nonirnage side of the support meterlal ln sliding contact. 

2. The method of claim 1 wherein said support material is maintained at a temperature sufficient to cause the powder image to fuse to the support material when contacted therewith.
 3. The method of claim 1 wherein said resilient member is comprised of a silicone gum rubber having a hardness ranging from about 15 to about 35 durometers cast on a flexible substrate.
 4. The method of claim 3 wherein the heat-fusible powder image is heated to a temperature below its fusing temperature.
 5. The method of claim 4 having the further step of pressing the support material into contact with sAid member with sufficient force to fix the powder image to the support material.
 6. In the process of xerography wherein an electrostatically charged xerographic plate is exposed to a projected light image to form an electrostatic latent image on the plate corresponding to the projected image and the plate is developed with heat-fusible toner particles attracted to the latent image to form a xerographic powder image corresponding to the projected image, the method of transferring and fixing the powder image to a paper support material comprising pressing a silicone rubber member into intimate contact with the powder bearing xerographic plate with sufficient force to cause the member to deform around said image, releasing the deforming force exerted on said member whereby the recovering resilient member enfolds the powder image therein, removing the image-bearing resilient member from the xerographic plate, heating a paper support material to a temperature sufficient to melt said xerographic powder when brought into contact therewith, and immediately pressing the heated paper support material into intimate contact with the image bearing resilient member with sufficient force to cause the powder image to adhere to the support material and become fixed thereto.
 7. Apparatus for transferring a xerographic powder image of toner particles from a photoconductive plate to a paper support material and fixing the image thereon including a resilient member arranged to be placed in contact with the photoconductive plate, means to exert a bias pressure on the resilient member into pressure contact with the photoconductive plate with sufficient force to cause the member to deform about the powder image for a predetermined time and then to release the deforming pressure exerted on said member whereby the member recovers sufficiently to entrap powder particles therein, means for transporting a paper support material into contact with the member carrying powder particles, and means to raise the temperature of the paper support material sufficiently immediately before contact of the support material with the powder particles such that upon contact said powder particles are transferred from the resilient member to the support material and fixed thereon.
 8. The apparatus of claim 7 wherein said member comprises silicone gum rubber having a hardness ranging from about 15 to about 35 durometers.
 9. Apparatus for transferring xerographic powder image from a rotating photoconductive drum to a final support material and fixing said powder image to the final support material including a resilient member being arranged to contact the photoconductive drum, drive means for moving said member at the same peripheral speed as the drum, means to place the resilient member into pressure contact with the drum with sufficient force to cause the member to deform about the powder image for a predetermined time and then, to release the deforming pressure exerted on said member whereby the member recovers sufficiently to entrap powder particles therein, means to move a final support material into contact with the powder image enfolded in said member, and means to heat the xerographic powder image while in contact with the final support material whereby the powder image coalesces to the final support material.
 10. The apparatus of claim 9 wherein said member comprises silicone gum rubber.
 11. The apparatus of claim 10 wherein said member is supported on a cylindrical drum.
 12. The apparatus of claim 10 including means to raise the temperature of the final support material to a level whereby the powder image being transferred is fused to said support material.
 13. The apparatus of claim 11 having further means to force the final support material into contact with the silicone gum rubber member with sufficient pressure to cause the heated toner to bond to the final support material.
 14. The apparatus oF claim 10 wherein the final support material is held in contact with the silicone rubber member by a heated platen arranged to support the nonimage side of the support material in sliding contact. 